Installing the Apache2 Web Server on the Raspberry Pi
With the Rasberry Pi connected to the Internet, update its local package database:
$ sudo apt-get update

Install Apache2:
$ sudo apt-get install apache2

When this has finished installing, CGI support is disabled by default.

Enter the following command:
$ ls /etc/apache2/mods-enabled/cgi*

If you don't see the following files:
/etc/apache2/mods-enabled/cgid.conf
/etc/apache2/mods-enabled/cgid.load

Then you need to enable the cgi module
Enable the cgi module by running a2enmod
$ sudo a2enmod cgi
$ sudo service apache2 restart

Now, you ask, "where do I put the programs / files?"
Your main web page will be here:
/var/www/html/index.html

Your CGI programs go here:
/usr/lib/cgi-bin

Resources:
https://httpd.apache.org/docs/2.4/howto/
https://httpd.apache.org/docs/2.4/howto/cgi.html

E-mail me: jim@merkles.com.